_Unciform Bone._ (_Os hamatum BNA_) (Fig. 51, _g_).--The unciform is a wedge-shaped bone with the apex of the wedge directed proximad, and smooth for articulation with the scapholunar. By a part of its ulnar surface it articulates with the cuneiform, and by its radial surface with the os magnum. Its distal end articulates with the fourth and fifth metacarpals. _Os magnum._ (_Os capitatum BNA_) (Fig. 51, _f_).--The os magnum may be described as an oblong plate bearing on its proximal surface a semicircular ridge which crosses it diagonally. The proximal end of the bone articulates with the scapholunar. Its distal end articulates with the third metacarpal except near its ventroulnar angle, where it articulates with the fourth metacarpal. Its ulnar surface articulates with the unciform. Its radial border articulates with the trapezoid, the third metacarpal, and, by two facets, with the second metacarpal. _Trapezoid._ (_Os multangulum minus BNA._) (Fig. 51, _e_).--The trapezoid is somewhat wedge-shaped, with the apex of the wedge pointing ventrad. Its proximal side articulates with the scapholunar, its distal side with the second metacarpal, its ulnar side with the os magnum, and its radial side with the trapezium. _Trapezium._ (_Os multangulum majus BNA._) (Fig. 51, _d_).--The trapezium has the form of a triangular prism curved into a semicircle. The convex face looks proximad and articulates by its ventral half with the scapholunar. The ulnar surface articulates with the second metacarpal dorsally, and ventrally with the trapezoid. Its radial surface articulates with the first metacarpal. =Bones of the Hand or Manus= (Fig. 51, 1-5).--The _Metacarpals_. _Metacarpus._--The metacarpals are the five bones of the palm of the hand; they are numbered from one to five, beginning with the thumb. They are cylindrical elongated bones with enlarged ends. The distal end is called the head, and the proximal end the base. Each head bears a hemispherical articular facet which is marked over its ventral half by a prominent smooth ridge. The surface dorsad of the ridge articulates with the proximal head of a phalanx. The ridge and the surface at its sides are for a pair of sesamoid bones. The first metacarpal (1) is the shortest. Its head is oblique, and it articulates by the ulnar half of its proximal surface with the trapezium (_d_); by the radial half with the radial sesamoid (_h_). The second metacarpal (2) is marked on the proximal part of its dorsal surface by an oblique groove passing from the radial side distad to the ulnar side. The base articulates with the trapezoid (_e_). The ulnar surface of the proximal end articulates with the os magnum (_f_) and third metacarpal, while the radial surface articulates with the trapezium (_d_).